Late Sunday night, Duquesne Light realized there was an issue with an underground power line that runs beneath the tunnel floor.

The repairs required crews to block the tracks on the right-hand side.

That forced all of the T trains up and over the Allentown Line throughout the morning rush hour and throughout the day, along with the buses that use the tunnel.

“And it should only be around a 10 minute delay, but during a rush hour type situation, it’s a little bit longer,” Port Authority spokesman Jim Ritchie said. “So, this morning, by the tail end of rush hour, we were looking at 20 to 30 minutes behind schedule.”

Duquesne Light finished repairs to the underground line on Monday evening. The Port Authority says regular service resumed in the tunnel around 8:45 p.m.